Conventionally, a brushless motor device is used as a driving source for driving an exhaust gas control actuator, such as an EGR valve used for vehicles or a VG turbo actuator. As methods of driving this brushless motor device, a 120-degree energization method, a 180-degree energization method, etc. are known. For example, in the 120-degree energization driving of a three-phase brushless motor, switching of coils to be energized is carried out every 60 degrees of electrical angle, and a non-energization period with an electrical angle of 60 degrees exists at the time of switching between the energizing directions of each coil. The 120-degree energization method has a feature of being able to reduce the influence of the detection of the rotor position and variations in the magnetization because of this existence of the non-energization period. Therefore, conventionally, the 120-degree energization method is typically used in many cases.
On the other hand, recent years have seen an increasing need for improvements in the responsivity of a brushless motor, though the use of the 120-degree energization driving having a non-energization period as mentioned above cannot satisfy the demands of users. For example, a drive controlling device for driving a brushless motor described in patent reference 1 controls the number of rotations of the brushless motor on the basis of a control parameter calculated according to the difference between a target number of motor rotations and the actual number of rotations, while controlling an energization phase angle on the basis of a detection signal showing the rotational position of the brushless motor. By thus correcting the energization phase angle of the driving circuit by using the control parameter for rotation number control, the drive controlling device ensures its responsivity to change in the number of rotations.    [Patent reference 1] JP,2005-192338, A
In order to improve the responsivity of the brushless motor, the energization phase angle can be corrected freely by using a rotational position sensor having a high resolution and a high-performance microcomputer, as shown in patent reference 1. However, in a low-cost system, a high-resolution rotational position sensor cannot be used.
FIG. 18 is a graph showing the degrees of responsivity of a 120-degree energization method and a 180-degree energization method which are used for a brushless motor having variations in a rotor rotational position sensor which can carry out detection every 60 degrees of electrical angle, and shows the results of performing simulations of the degrees of responsivity which the 120-degree energization method and the 180-degree energization method exhibit until the position of a rotor reaches its target position in the case of changing the above-mentioned target position step by step. In this case, a curved line denoted by a reference character A in FIG. 18 shows the result of the simulation of the degree of responsivity of the 120-degree energization driving (an advance angle of 0 degrees), and a curved line denoted by a reference character B in FIG. 18 shows the result of the simulation of the degree of responsivity of the 180-degree energization driving (an advance angle of 0 degrees).
In FIG. 18, the degree of responsivity of the 180-degree energization driving (an advance angle of 0 degrees) is slower than that of the 120-degree energization driving (an advance angle of 0 degrees). The 180-degree energization method thus has a wide energization width, though the 180-degree energization method exhibits a lesser degree of responsivity compared with that of the 120-degree energization method until the position of the rotor reaches the target position, as shown in FIG. 18. Therefore, even if switching between energization methods having different degrees of responsivity is simply carried out, any desired degree of responsivity cannot be provided.
The present invention is made in order to solve the above-mentioned problem, and it is therefore an object of the present invention to provide a brushless motor device that improves the responsivity of a brushless motor by properly switching between a 120-degree energization method and a 180-degree energization method, and a control device which controls the driving of the brushless motor.